1. Field of the Invention:
The present invention relates to an EL-combined sheet switch to be used, for example, in an inputting device for portable telephones, electronic pocket-books, etc.
2. Description of the Related Art
Portable appliances such as portable telephones, electronic pocketbooks, notebook-type personal computers, etc., in which an additional backlight is provided in the switch key area so as to facilitate the key operation even in the dark are known.
For example, in a portable telephone, a thin EL device is disposed as the backlight source in the side of the back surface of a switch key board. Through-holes are provided in the site of the EL device that correspond to switch keys. In this construction, when a switch key is pressed at its front surface, it is electrically connected with the EL device through the through-hole, and after the pressure is released, the electric connection is cut off. In this manner, the switch keys are lighted through light emission around the through-holes, allowing the keys to be differentiated even in the dark.
Ordinary EL devices emit light in the electric field of an alternating current, and generate electromagnetic noise. Therefore, electronic appliances equipped with an EL-combined sheet switch will often malfunction because of the electromagnetic noise generated by the EL device.